Sewage treatment plants

ABSTRACT

An automatically regulated plant for the treatment of sewage comprises a primary feeding tank for receiving liquid raw sewage, a pump immersed in said primary tank to feed the plant with the liquid discharged in the tank, means for controlling the operation of the pump, at least one digester with biologically active filter bed, means to convey a certain amount of the outflow of the treated effluent from said digester to the primary feeding tank, a valve for controlling the flow of the recirculated effluent, a program timer correlated with the means to control the operation of the pump and adapted to actuate the recirculation valve and to cause said valve to be drived into its open position after expiration of a delay period following the stopping of the pump.

D United States Patent 1 1 3,563,382

[72] Inventor J J h R e t [56] References Cited Nantes, France UNITEDSTATES PATENTS [2 pr 7823" 1,820,977 9/1931 lmhoff 210/195 1 PMDec-11,1968 2,574,685 11/1951 Baxteretal... 210/195 51 PatentedFeb-16,1971 3,207,313 9/1965 Schulze 210/195 1 Assignee p 3,242,0713/1966 Walker 210/138X scl'vlcesoverah'mmlwmmmemm 3,397,789 8/1968Valdespino 210/195X France-Compagnie S D A F lssy Les Moulineaux(Seine), France [32] Priority Dec. 12, 1967 [33] France [31] 131,846

[ 1 sew EEZR ANIS 1 Claim, 2 Drawing Figs.

Primary Examiner-JohnAdee Att0rney-Christen & Sabol A BSTRACT: Anautomatically regulated plant for the treatment of sewage comprises aprimary feeding tank for receiving liquid raw sewage, a pump immersed insaid primary tank to feed the plant with the liquid discharged in thetank, means for controlling the'operation of the pump, at least onedigester with biologically active filter bed, means to convey a certainamount of the outflow of the treated efiluent from said digester to theprimary feeding tank, a valve for controlling the flow of therecirculated effluent, a program timer correlated with the means tocontrol the operation of the pump and adapted to actuate therecirculation valve and to cause said valve to be drived into its openposition after expiration of a delay period following the stopping ofthe pump.

Patimked Feb. 16, 1971 2 sheets-sheet 1 Patented Feb. 16,1971 v3,563,382

2 Sheets-Sheet 2 1 EWAGE TQEATMENT BLANTS The present invention relatesto biologically active plants for the treatment of raw sewage.

It is known that in plants of the above type the effluent afterappropriate treatment is subjected to a partial recirculation so as toallow:

the sludge to be discharged and conveyed to the digester;

the biologically active bed to be continuously cleansed due to thehydrostatic pressure in it; and

the final effluent to be discharged (for instance to a stream) aftersufficient cleansing and as a clear, relatively harmless liquid.

It is fairly simple to time the'recirculation flow; for instance if theraw sewage and treated effluent pour in a common tank where an immersedpump is adapted to feed the plant with the mixed liquid the starting andstopping of this pump can be controlled by a clock. However this deviceis only valid under these conditions that the inflow of raw sewage isnearly constant.

As a matter of fact these conditions rarely occur; the above devicelacks flexibility and is not adapted to the various changes in theinflow of raw sewage, both according to the hour of the day andaccording to the season of the year.

Since the recirculation flow is independent of the sewage inflow it willbe often either insufficient when the sewage inflow is low, or in excesswhen the sewage inflow is subject to a considerable and quick increase.

It is desirable for the sewage treatment plants with a biologicallyactive filter bed, to work with the following conditions:

1. The flow of liquid with which the plant is fed during a period oftime is maintained to an amount corresponding to the optimal flowcalculated for the plant, considering the biological and hydraulicconditions.

2. This optimal flow should be maintained irrespective of the inflow ofthe raw sewage conveyed to the plant by the sewer network, i.e.irrespective of the total amount of raw sewagedischarged to the plantduring the same day and irrespective of the head flow arriving in theplant.

3. This optimal flow should be constant so that the plant is fed asregularly as possible.

To have these conditions complied with it is necessary for the treatedeffluent to be recirculated with a flow adapted to the amount of rawsewage discharged by the sewer network, the flow of recirculatedeffluent being inverse of the amount of raw sewage pouring into thefeeding tank.

Some devices are known that intend to obtain the desired result above:

1. The starting and stopping of the pump is controlled by a clock asindicated above; such a device entails these disadvantages that the flowof recirculated effluent is constant irrespective of the flow of rawsewage whereas the desired result is to cause the flowof recirculatedeffluent to increase when the inflow of raw'sewage decreases and viceversa.

2. In other plants a float device in the feeding tank actuates theopening and closing of the valve controlling the recirculation of thetreated effluent; however in such devices the total amount ofrecirculated effluent is out of control and furthermore the flow ofliquid pumped in the feeding tank and conveyed in the plant is notregulated.

3. The valve may be actuated by a special float device so that therecirculation valve is opened as soon as the immetsed pump in thefeeding tank stops and it is driven to its closed position when theliquid in the feeding tank has reached a level corresponding to thefloat device; then since the recirculation valve isclosed, the furtherfilling of, the feeding tank results from the pouring in of the rawsewage along until the liquid reaches an upper float device actuatingthe starting of the pump; in this device a lower float actuates thestopping of the pump, the special float device actuating therecirculation valve being situated at a level intermediary between thelower and upper floats adapted to actuate the starting and stopping ofthe pump.

This device, though it is more convenient than the ones previouslyspecified, does not completely fulfill the requirement; therecirculation is takes place even though the inflow of raw sewage hasincreased to a high value; on the contrary when the inflow of raw sewagehas stopped for some time the filling up of the feeding tank does notallow the liquid to reach the upper float device so that the pump is notactuated and the plant is not fed with liquid to be treated. Further itis necessary in such a device to modify the regulation of the system(i.e. the level of the intermediary float in the feeding tank) if andwhen the flow of raw sewage turns out to change.

It is an object of this invention to provide a sewage treatment plantwith a biologically active filter bed that obviates the disadvantages ofthe known plants.

Other objects and advantages of the invention will be apparent from thefollowing description taken in conjunction with the accompanying drawingin which:

FIG. 1 is a largely schematic view representing a vertical cross sectionthrough a digester and a primary feeding tank embodying the majorfeatures of this invention; and sewage disposal unit according to theinvention.

As seen in FIG. 1, the present invention relates to an automaticallyregulated plant for the treatment of sewage comprising a primary feedingtank 52 for receiving liquid raw sewage via 51, a pump 53 immersed insaid primary tank to feed the plant via 55 with the liquid dischargedinto the tank, means for controlling operation of the pump, at least onedigester 54 with a biologically active filter bed, means 56 to convey acertain amount of the outflow of the treated effluent from said digester54 to the primary feedingtank 52, a valve 57 controlling the flow ofrecirculated effluent, a program time 63 correlated via 61 and 62 withthe means to control the operation of the pump and adapted to actuatevia 65 the recirculation valve 57 and to cause said valve to be drivenin open posi tion after expiration of a delaying period following thestopping of the pump.

Means for controlling the operation of the pump 53 consist of two floatdevices as specified above; the upper float device 60 causes the pump 53to start via 62' and the lower float device 59 actuates the stopping ofthe pump 53 via 61'.

Accordingly when the level of the liquid in the primary feeding tank 52has reached the level ofthe upper float device 60 the pump 53 starts andthe primary tank is discharged until the level of the liquid has reachedthe lower float device 59 which results in the stopping of the pump 53.

The program timer 63 is correlated with the operation of the pump; thedelay period begins with the stopping of the pump, and at the end ofthis delay period the program timer actuates the opening of therecirculation valve 57.

The program timer 63 is correlated with the means for controlling theoperation of the pump so that it causes the recirculation valve to beclosed when the pump starts and the program timer is so arranged that itreturns automatically to zero in the case that before expiration of thedelay period, the liquid in the feeding primary tank due to the inflowof raw sewage in 51, has reached the level of the upper float device 60corresponding to the starting of the pump.

According to the invention, the smaller is the inflow of raw sewage 51,pouring into the primary tank 52, the less quickly the liquid in saidprimary tank will reach to the level of the upper float device 60causing the pump to start; accordingly the program timer 63 will, afterexpiration of the delay period, allow the recirculation valve 57 to beopened and the outflow of recirculated treated effluent to fill theprimary tank 52.

Even though the inflow of raw sewage turns out to be zero, therecirculated effluent will fill up the primary tank so as to avoid theplant not to be fed.

On the contrary in the event that the inflow of raw sewage becomesgreater it will more quickly fill up the primary tank, and when theprogram timer actuates the recirculation valve, the primary tank will bealmost filled up so that the recircula tion will take place but for ashort period of time, until the starting of the pump causes therecirculation valve to be closed. It may occur that the inflow of rawsewage is so great that the primary tank is filled up before the delayperiod has come to an end; accordingly the pump starts without theeffluent having been allowed to be recirculated.

It is understood that in such a device the flow of recirculated effluentis inversely proportional to the flow of raw sewage, which correspondsto the desired operative conditions of the plant.

In MG. 2, the raw sewage is conveyed by the sewer pipes 2 and 3 with theman hole 1 and pours into the primary feeding tank 6 in which areimmersed the pump 7, which pumps convey the liquid of the primary tankto the tanks 14 and 15 through the pipe 11; hence the pipe 16 conveysthe liquid to the biologically active filter bed 17, from which theliquid is directed to the decanter 23, through the pipes 18 and 22 witha man hole 19; the pipe 24 with a further man hole 25 conveys theeffluent as a relatively clear liquid to the outflow pipe 27 receivingthe overflow from the hole 1.

The plant comprises a set of sludge areas 31 and 32 receiving the sludgefrom the tanks 14 and 15 respectively through the pipes 33 and 34 withthe valves 37 and 38 and the man holes 35 and 36.

The recirculation of the treated effluent is provided by the pipe 41coming from the decanter 23 and discharging said effluent in the primarytank 6 through the recirculation valve 42. This valve 42 is undercontrol of the program timer 43 which is electrically bound to the pumpoperation control device, so that the recirculation valve is actuatedinto its open position after a predetermined delay following thestopping of the pumps.

After the expiration of this delay period the valve 42 is caused to beopened and remains so as long as the pumps remain out of operation; assoon as the level of the liquid in the primary tank brings about thestarting of the pumps the recirculation valve 42 is caused to be driveninto its closed position.

I claim:

1. In an automatically regulated plant for the treatment of sewagecomprising: a primary feeding tank for receiving liquid raw sewage; atleast one digester with a biologically active filter bed; a pumpimmersed in said primary tank to feed the digester with the liquiddischarged in the tank; float means for controlling the operation of thepump, said float means being adapted to stop the pump when the sewagelevel in said primary feeding tank reaches a predetermined lower leveland to start the pump when the sewage level in said primary tank reachesa predetermined upper level higher than said predetermined lower level;means to recirculate a portion of the outflow of the treated effluentfrom said digester to the primary feeding tank; and a valve controllingthe flow of recirculated effluent, the improvement which comprises aprogram timer correlated with the float means and actuating therecirculation valve for closing the valve when the float means startsthe pump, and for opening the valve at the expiration of a determineddelay period following the last stopping of the pump, the program timerbeing returned to zero by the float means when said float means startsthe pump, whereby if the float means has restarted the pump before theexpiration of the determined delay period, the timer will allow thevalve to remain open.

